Spatial variation of climatology monthly crop reference evapotranspiration and sensitivity coefficients in Shiyang river basin of northwest China

In the cool months (January, February, November and December), the spatial variability of ET0 is small and the value is rather low, whereas the warm season (May, June, July and August) is characterized by high values of ET0 and large spatial variations in the river basin. Vapor pressure deficit is the most sensitive variable during the cool months and in the mountainous area with lower temperature; mean air temperature is the least sensitive one during the year and a little variation is observed at the basin scale. In summer, available energy primarily forces ET0 as expected, and in winter, wind speed plays an important role and affects ET0 greater at the northern plain region where deserts are dominated by dunes and low shrubs. We conclude that for regions with isolated climate stations, 'IC' procedure by including topographic and geographic factors can effectively model spatially distributed ET0.